Pot odds explained

A lot of the money to be made in poker comes from players who chase draws in small pots.  Most of the time, draws do not come through, so the money spent on calls is lost.  When a draw hits, there must be enough money in the pot to make up for all those times it didn't.  Enter the concept of "pot odds." 

The money in the pot must be greater than the odds of completing a draw. 

For example, you are on the button and flop an inside straight, 6♥7♠_9♣T♥.  There are three bets in the pot; a bet and a raise make the total six.  To chase your draw, you must call two bets.  The pot odds are thus 6:2, e.g. 3:1.  The chances of completing an inside draw with the next card are 11:1.  With pot odds of only 3:1, this is a very unprofitable draw.  If you chase hands like that you will leak money like a sieve.

Now let's take the same hand, but with different pot odds.  Say there are more people in the pot, and no raise.  When it gets to you, there are 13 bets in the pot, and it costs only one to call.  Now with pot odds of 13:1, it is a profitable draw.

FYI, here is how the 11:1 odds for an inside draw are derived.  In the above hand, only four cards in the deck (the eights) complete a straight.  There are 47 unseen cards left in the deck.  4/47= 12 (rounded).  So on average, if 12 cards are drawn from the deck, one of them will be your blessed eight.  Eleven cards are not eights, one card  is an eight, giving odds of 11:1. 

A much better draw is an "open ended" straight.  Say you flop the hand 6♥7♠8♠9♣.  Now eight cards will help -- the tens and fives.  Look down the "outs" column in the chart on the right until you find "8".  If you have eight outs, you need pot odds of only 5:1.

Here's an atrocious draw.  If you have a low pair, say 66, only two cards will improve it, requiring pot odds of 23:1.  So if you hold 66, and there's a K and Q on the board, and people are betting, you would never call in limit holdem without xray vision.

More complications: implied odds.